The term “spectra” describes the distribution of light energy across a continuous range of wavelengths. The reflectance spectrum (also known as ‘spectral signature’) of a material, which includes the proportion of light reflected from it, is a characteristic of the material.
The development of image sensor technology has made it possible to capture image data covering a broad spectrum of wavelengths. In contrast with trichromatic sensors, multispectral and hyperspectral sensing devices can acquire wavelength-indexed reflectance and radiance data in hundreds to thousands of bands across a broad spectrum. To date, these spectra are acquired and stored in discrete wavelength-indexed measurements.
As a result, the size of reflectance or radiance spectrum data is dependent upon the number of wavelengths, or spectral resolution. For high-resolution spectra, each signature can consist of hundreds of values, i.e. bands, that require large storage spaces in order to be stored.